1. Field of the Invention
This invention relates to capacitive type proximity sensors, and more particularly to robotically positioned devices including capaciflector proximity sensors.
2. Description of the Prior Art
Capaciflector technology involves a capacitive proximity sensing element backed by a reflector driven at the same voltage as and in phase with the sensing element. The reflector is used to reflect electrical field lines from the sensor away from a ground plane and towards an object being sensed. Such a device is shown and described in detail in U.S. Pat. No. 5,166,679, entitled, "Driven Shielding Capacitive Proximity Sensor" granted to John M. Vranish et al on Nov. 24, 1992.
A phase discriminating capacitive type sensor array system which includes multiple capaciflector sensor elements which are maintained at a phase and amplitude based on a frequency reference provided by a single frequency stabilize oscillator is also known and is shown and described in U.S. Pat. No. 5,214,388, entitled, "Phase Discriminating Capacitive Array Sensor System", granted to John M. Vranish et al on May 25, 1993.
In U.S. Pat. No. 5,373,245 granted to John M. Vranish on Dec. 13, 1994, entitled, "Capaciflector Camera", there is disclosed a sensor system wherein a capaciflector array consisting of multiple rows and columns of capaciflector sensor elements enables a device to generate close-in images of the object being sensed as it is approached, for example, in a berthing or docking maneuver as well as providing an invaluable aid in obstacle avoidance in navigation.
An electronic circuit which has been found to be particularly useful in capaciflector apparatus, is a circuit element known as a current-measuring voltage follower circuit. This circuit enables current changes in the sensor and shielding elements of the capaciflector to be accurately sensed without cross talk between neighboring elements and/or their electrical leads. Such circuitry is further shown and described in detail in above referenced related application Ser. No. 08/187,344, entitled "Current-Measuring Op-Amp Devices".
Heretofore robotic berthing and docking operations in free space lacked any substantial precision. This has led to unexpected and imprecisely predicted minor collisions during the berthing/docking procedures which are not helpful to the precision scientific instruments on board. Safety has also been compromised. The most dangerous aspect of conventional systems is that with the extensive use of passive compliances and relatively large mechanical error corrections made by alignment cones, mechanical energy is stored and as a consequence the system can easily jam or lurch upon removal. With this undesirable possibility comes damage and mission failure. Passive compliances also lead to spongy, imprecise handling characteristics when the payload is being transported from one position to another in space.
Also this approach has classically been based on camera views backed up by a computer world model. With such techniques, there are always those safety issues caused by limitations of the camera view and discrepancies between the world model and hardware. Additionally, sensory field-of-view obstructions and lighting distortions and limitations can seriously handicap robotic operations. For example, present state-of-the-art apparatus cannot see very near the point of contact. Thus, if a cone is not exactly in the correct place or if a fastening hook is ajar, it would not be possible to detect this. All that would be known is that the operation has not been successful. In the subject invention, however, the apparatus in effect "views" a berthing hole, for example, from the viewpoint of the pin being inserted and as a result there are no obstructions.
With the large sizes of alignment cones and tool pins and passive compliance required, the number of applications are necessarily limited. For example, at present an entire end effector must be exchanged if the end-point of the robot tool is changed. With the subject invention, only the tool bits need be changed.